U.S. Pat. No. 3,623,627 to Bolton discloses a door construction for a pressure vessel. As shown by Bolton, the vessel has two openings each of which is closed and sealed by means of a door member mounted on tracks which are secured to the interior wall of the pressure vessel. Each opening is surrounded by a seal assembly having a grooved member on the interior surface of the vessel such that when the door is closed, the door member is urged against the grooved member by cam members attached to the tracks. The seal assembly then is urged into contact with the adjacent surfaces of the door member to provide a pressure tight seal between the door member and the vessel wall. There are several drawbacks to the door construction disclosed by Bolton. First and foremost, the design and configuration of the interior mounted tracks significantly restricts the size of the door member which in turn restricts the size of the opening, thereby limiting access to the interior of the vessel and limiting the size of a container which can be placed within the pressure vessel. In addition, Bolton does not provide any means to interlock the door's edges between the track's guide rails, thereby restricting the distance between track's guide rails and preventing a high length to width ratio of the door dimensions. Thus, Bolton's door construction can not be applied to large openings in tall cylindrical pressure vessels. Further, in order to transfer the forces of pressurization to the edge of the door opening of the pressure vessel, Bolton's door construction must be located on the interior surface of the vessel, again limiting the size of the door opening. Bolton's configuration also requires that the addition of special cam members having inclined surfaces to be secured to the tracks in order to seal the opening; these cam members interact with the door member's wheels in order to urge the door member laterally away from the track and into contact with a seal holder. Moreover, the interior mounting of the door construction not only exposes the door member and it's tracking mechanism to any corrosive or deleterious vapors in the pressure vessel, but also obstructs and interferes with the mounting and use of wall attachments located on the interior surface of the pressure vessel.
U.S. Pat. No. 3,050,211 to Hutterer discloses a washing machine door having a curved shell door slidably mounted on runners on the exterior surface of the washing mean. The door is provided with a flexible sealing member which can be inflated in order to provide a "fluid tight" seal for the washing machine. However, the curved door is not designed to transfer the load from the washing machine to the door and guide track.
Despite the teachings of the prior art, a need still exists for a closure assembly for sealing a pressure vessel which can accommodate various size tanks, including, for example, large tanks capable of housing a 55 gallon drum and should be designed to provide coverage of very large door openings relative to the size of the pressure vessel. Such a closure assembly should be capable of quickly and efficiently creating a pressure tight seal between the vessel and the closure. Moreover, such a closure assembly should be mountable in such a manner that it does not require the use of hinges or latches and does not necessitate door swing. In addition, such a closure assembly should be configured in such a manner that the forces of pressurization are transferred from the door to the pressure vessel.